The present invention relates to a flood control system for a dam having a small capacity. The flood control system is provided particularly for a dam such as a sub-dam, a single dam, a main dam, a connective dam of the main dam, etc.
Prior art flood control systems have been constructed on the basis of a combination of the following controls (1) to (9).
1. Preparative Water Flow Control
The water level is previously lowered by way of precaution against an expected flood.
2. Beforehand Water Flow Control
Even if the water level is less than a reference level when the inflow has begun to increase, a certain quantity of the water flow is previously discharged.
3. Constant Water Level Control
The optimum water level is determined in view of the river conservancy and the water utilization and the water level is controlled so that it is maintained in a constant permissible region.
4. Constant Water Flow Control
A constant quantity of water is continuously discharged when the inflow exceeds a predetermined quantity.
5. Set Point Control of Gate Angle
The angle of the gate is controlled so that it coincides with the target angle thereof.
6. Outside Control
The gate is controlled in response to the command angle given from the outside, for example, from the water control center.
7. Constant Proportional Control
When the inflow exceeds a reference level, the water is discharged in proportion to the overflow.
8. Variable Proportional Control
The overflow is discharged at a variable rate.
9. Special Rule Control
The water level is collectively controlled in response to information, such as the rainfall on the upstream side of the dam, the water level of the dam on the river, the margin of the pondage, etc.
When such a prior art system is adopted for use with a dam having a small reservoir capacity, the following problems arise:
1. In a dam where the submerged area and the reservoir capacity are small as compared with the catchment area, the water level has the tendancy to abruptly change. Therefore, it is difficult to react promptly enough to maintain the water level within a permissible range.
2. In a dam where the control range of the water level is small as compared with the inflow, for example, where a hydraulic power plant is provided, it is required to maintain the water level at a level near the level of the filled water. Therefore, high control accuracy is required for the control of the water level.
3. According to constraints of dam control, the following rule has been adopted. Under normal conditions, the outflow Q.sub.c [m.sup.3 /s] at any time is defined by the following equation: EQU Q.sub.c = a .sup.. Q.sub.ct + b
Q.sub.ct [m.sup.3 /s] represents the outflow for the previous t minutes before the present time, and a and b represent coefficients determined by various parameters of the dam.
In a flood condition, the outflow is restricted so that the outflow never exceeds the inflow and the water level is within the permissible region. Therefore, it is difficult to control the water level so as to satisfy the constraints of the dam control.